1. Field of the Invention
The present invention relates to an exercise device that provides resistance when pulled. More particularly, the invention relates to an exercise device that provides two or more levels of resistive force.
2. The Prior Art
Exercise devices are known from the prior art, for example, spring-biased expanders. With the known expanders, muscles can be trained by expending power to oppose and overcome the biasing force of the spring. Initially, the spring provides a low resistance, but the resistance increases, in accordance with the spring characteristics, as the spring is further pulled apart or compressed. The resistive force of the spring, which increases more or less linearly, only stresses the red muscle fibers. The white muscle fibers, which are responsible for explosive force, are not stressed by the known devices.
Therefore, it would be advantageous to have an exercise device which provides at least two stages of resistive force, for stressing both the white muscle fibers and the red muscle fibers.